Field of the Invention
The present invention relates to a laser processing method of removing a portion of an object to be processed using layer light.
Up to now, when holes or grooves are to be formed in a substrate, for example, a semiconductor material substrate, a glass substrate, or a piezoelectric material substrate, which is an object to be processed, the substrate is irradiated with laser light by a generally known laser processing method for removal and processing. In such a kind of laser processing method, a laser light irradiation time necessary for laser processing of the substrate is normally determined based on a result obtained by trial processing. Even when a correct laser light irradiation time is determined based on the result obtained by trial processing, however, a removal depth may fluctuate due to fluctuations in thickness of the substrate and the surface area.
As measures to solve such a problem, there may be conceived such a laser processing method as described in Japanese Patent Application Laid-Open No. H02-092482. In this laser processing method, a substrate is made of different materials, for example, an insulating material and a metal material. When a change in reflectance of laser light on the metal material is detected while the insulating material is laser-processed, processing with the laser light is stopped. Therefore, holes may be formed only in the insulating material.
In the conventional laser processing method described above, however, the object to be processed is an object that includes a processed portion and a non-processed portion that are made of different materials (for example, a printed circuit board, in which steel material is buried). When the object to be processed is made of for example, a single material (for example, a Si wafer), the laser processing method described above cannot be applied. In the conventional laser processing method described above, a processing shape is determined depending on a shape of the non-processed portion, and, hence, the degree of freedom of processing is low.